Shrewd; sagacious (6)
I believe the answer is:
astute
I believe this is a double definition.
'shrewd' is the first definition.
(I know that shrewd can be written as astute)
'sagacious' is the second definition.
(I've seen this in another clue)
(Other definitions for astute that I've seen before include "Shrewd, wily" , "Wise" , "Statue (anag)" , "Discerning" , "Shrewd and sagacious" .)